A challenge for the formulation chemist is to prepare a physically stable topical pharmaceutical composition where the active ingredient is also found to be chemically stable. Such pharmaceutical compositions should:    (i) not irritate the skin,    (ii) be specifically adapted to deliver the active ingredient onto or into the skin so as to treat a particular dermatological condition or disorder,    (iii) be cosmetically elegant to ensure that the patient complies with the prescribed treatment regimen,    (iv) provide penetration of the active ingredient to the appropriate layers of the skin and engage the desired target, and    (v) minimize systemic exposure while achieving local dermal/epidermal delivery.
One active ingredient of interest to be formulated in a physically and chemically stable topical composition is 3,5-Dihydroxy-4-isopropyl-trans-stilbene which has the following formula:

This compound is also known as 5-[(E)-2-phenylethenyl]-2-(propan-2-yl)benzene-1,3-diol or 2-(1-Methyethyl)-5-[(1E)-2-phenylethenyl]-1,3-benzenediol.
3,5-Dihydroxy-4-isopropyl-trans-stilbene is believed to have been originally disclosed by Paul et al., Journal of Chemical Ecology 1981 7(3): 589-597 as an antibiotic. Li et al, Applied and Environmental Microbiology 1995 61(12): 4329-4333 also isolated the compound, but from a different bacterial strain and further demonstrated its fungicidal activity. The fungicidal activity of the compound was also described in WO 1995/003695 (Agro-Biotech Corporation). The compound is further described in WO 2001/042231 (Welichem Biotech Inc.) and in U.S. Pat. No. 7,868,047 and as being suitable for the treatment of various key dermatological conditions including psoriasis and inflammation. Example 3 of the U.S. Pat. No. 7,868,047 patent describes a cream formulation with an active ingredient being made in Galax Base. Applicants have been unable to ascertain any compendial notations or availability of a commercial cream base called “Galax” and therefore its composition remains unknown.
3,5-Dihydroxy-4-isopropyl-trans-stilbene is known to be sensitive to oxidation and photo degradation (see e.g. Gao et al., Journal of Polymer Research 2011 18: 1501-1508). Accordingly, there remains a need in the art for a topical composition comprising 3,5-Dihydroxy-4-isopropyl-trans-stilbene that is both chemically and physically stable, which delivers the active ingredient to the desired site of action in the epidermis and/or dermis, and which does not irritate the skin in use.